docs: def purview(repertoire):
      """The purview of the repertoire.
  
      Args:
          repertoire (np.ndarray): A repertoire
  
      Returns:
          tuple[int]: The purview that the repertoire was computed over.
      """
      if repertoire is None:
          return None
  
      return tuple(i for i, dim in enumerate(repertoire.shape) if dim == 2)